The amino acid content of sake koji was analyzed by preparing eighty-five kinds of koji samples in separate petri dishes using five kinds of rice varieties and seventeen kinds of koji strains. The amount of amino acids formed in the sake koji making process was also estimated. Amounts of mycelia, enzyme activity, and amino acid totals of 85 koji samples were analyzed by variance, discrimination, and cluster analyses. The findings are as follows: (1) Koji samples abundant in residual amino acids showed high enzyme activity. (2) About 80% of the amino acids formed from steamed rice were utilized by the koji mold while 20% remained in the koji. (3) The major residual amino acids of the koji were glutamine and arginine. (4) The quantity of residual amino acid in koji may be reduced by half with on optimal combination of rice variety and koji mold strain.
Monthly mean temperature anomalies in August and September from 1998 to 2010showed a positive correlation with the national mean data of sake cake ratios. The average enzyme digestibility of 7 rice cultivars showed negative correlations with the national mean data of sake cake ratios. Gelatinization temperatures measured by differential scanning calorimetry (DSC) showed positive correlations with the national mean data of sake cake ratios. The obtained results suggest that atmospheric temperature conditions during the grain-filling period of material rice strongly affect the digestibility of steamed rice grains in sake mash because the structure of amylopectin is influenced by atmospheric temperature conditions during grainfilling.